The present invention relates to mechanical fasteners, such as screws, bolts, pins, etc., that utilize a difference in thermal coefficients between the fastener and surrounding material (e.g., a threaded housing or a passage) to create a seal and maintain the mechanical fastener secure in extreme temperatures.
High temperature and/or high pressure environments present challenges for fasteners such as screws, bolts, pins, etc. that are relied upon to provide a seal and/or to remain secure. For example, in hydrocarbon production wells, it is often beneficial to regulate the flow of formation fluids from a subterranean formation into a wellbore penetrating the same. A number of devices known as inflow control devices (“ICDs”) are available for regulating the flow of formation fluids. Some ICDs are simple on/off valves, others are metered to provide a desired flow rate, and still others discriminate between different types of formation fluids. ICDs can include, for example, tubular flow restrictors and nozzle-type flow restrictors.
It is common for nozzle-type ICDs operating at extreme high temperatures and pressures to include housings with passages into which an adjustable rod can be inserted to block or adjust fluid flow. A set screw or other threaded fastener is typically used to close off the end(s) of the passage and retain the rod in the passage. At high temperatures, the screw(s) can often become loose and/or allow leakage into or out of the passage due to thermal “growth” of the housing, which is typically made of steel or another material similar to that of the screw(s).
To prevent leaking and loosening of threaded fasteners, chemical sealants such as LOCTITE™, and mechanical means such as safety wire, screws, or O-rings have been used in the past. However, these conventional sealing and thread locking schemes often are not adequate to prevent leakage at extremely high temperatures.